Tosefta for Numbers 18:34

Said Rabbi Nechemiah, why is everyone trusted as to [the purity of the articles involved in] the purification rite [involving the red heifer] and as to consecrated food ("נאמנין על בהחטאת ועל הקדש", see Lieberman), but not everyone is trusted as to Terumah? So that people will not say, "Behold, I am building an altar for myself," or "Behold, I am burning a red heifer for myself," as it is said (Num. 18:7), "And you (=Aaron) and your sons with you shall safeguard your priesthood in every matter [regarding] the Altar..." (See Chag. 22a:15.) One might say that [the word "safeguard" includes] even [Terumah,] Terumat Ma'aser (the priestly portion taken from a Levite's tithes) and Challah (the portion of dough set aside for the Kohen), [and thus] the Torah comes to teach "... and to [that which is] within the Curtain." What is special about that which is "within the Curtain" is that it is not familiar to [the non-priestly class of] Israelites [who are forbidden from entering the area beyond the Curtain], which thus excludes Terumah and Terumat Ma'aser and Challah, with which Israelites are familiar. Rabbi Yehuda says, behold, it says [in regards to the red heifer] (Num. 19:9), "and it shall be for the congregation of the Children of Israel to safeguard it as the waters of purification...", such that everyone should be trusted as to safeguarding it. [If there is] a doubt as to the status of an am ha'aretz as regards to [the impurity of] treading or movement [of a zav (see Niddah 43a:3)], [they are deemed] pure as to matters of chullin and impure as to matters of Terumah.

One who takes terumah from grapes to be made into raisins (Ter. 1:9), or figs to be made into dried figs, or pomegranates to be made into dried pomegranates (פֶּרֶד not כרי, see Jastrow), it is [valid] terumah and he need not take terumah a second time. Rabbi Eliezer says, Beit Shammai say that he need not take terumah a second time, and Beit Hillel say that he needs to take terumah a second time. Beit Hillel said to Beit Shammai, behold, it says (Num. 18:27), "[your terumah will be reckoned] like fully-fermented [grapes] from the vat" (see Ter. 1:10). He does not take terumah of this (i.e., of dried fruit) from the vat. Beit Shammai said back to them, behold, it says (Lev. 27:30), "And every tithe [of the land, whether from the seed of the land [or] the fruit of the tree, is for God, it is holy to God." If you say, that he needs to take terumah a second time, therefore [the first terumah] will not remain holy to God.

One who brings ears of grain inside his house in order to rub off the chaff (=מלילות, see Maasr. 4:5), behold, he [may] take terumah [of the ears of grain in that state]. A Levite for whom ears of grain were designated, to in the future make a threshing floor with them, [or] grapes to in the future make them into wine, [or] olives to in the future make them into oil -- just as the first terumah (Num. 18:12) is taken from the threshing floor and from the vat, so too the terumah of tithes is taken from the threshing floor and from the vat.

[In summary,] we [may] separate terumah and tithes from the impure on behalf of the impure, and from the the pure on behalf of the pure, and from the impure on behalf of the pure, but not from the pure on behalf of the impure (contrary to Rabbi Eliezer above (and see Bava Kamma 115b:14)). Rabbi Nehemiah says, we do not separate [terumah] from the impure on behalf of the impure, but only as to demai. They said to him, behold, it says (Num. 18:28), "... and [they] are to give from them the contribution of God to Aharon the priest" (i.e., the Torah does not distinguish between pure and impure in relation to terumah).

[With respect to] Kohanim and Levites who were assisting between threshing floors, [the landowners should] not give them Terumah and tithes [as part of] their salary, and if they gave them, behold, they are [deemed] unconsecrated [produce], as it is said (Num. 18:32), "and you shall not profane the sacred donations of the Children of Israel," [and treated as though] they were already unconsecrated. And it is said (Mal. 2:8), "You corrupted the covenant of the Levites, said the Lord of Hosts." More than this, they (i.e., the Sages) said, "Their Terumah is not Terumah and their tithes are not tithes," and not only that, but the Sages [also] sought to punish them such that they would need to separate Terumah from their own produce. And about them it is written, saying (Micah 3:11, JPS tr.), "Her rulers judge for gifts, Her priests give rulings for a fee, [And her prophets divine for pay]," and therefore God brought on them three punishments corresponding to their three sins that they committed, as it is said (Micah 3:12, JPS tr.), "Assuredly, because of you, Zion shall be plowed as a field, [And Jerusalem shall become heaps of ruins, And the Temple Mount a shrine in the woods]."